A capacitor of capacitance ‘C’ is fully charged by a $200\;V$ supply. It is then discharged through a small coil of resistance wire embedded in a thermally insulated block of specific heat $2.5 \times 10^2 \;J kg^{–}1k^{–1}$ and of mass $0.1\; kg$. If the temperature of the block rises by 0.4k, the value of C is